New building standards designed to protect Western Australia homes from deadly bushfires have been criticised as expensive and difficult to implement.

The new standards will require many new homes to be assessed based on location, topography and type of bush surrounding the home and will come into effect from April.

They cover key elements in homes including external doors and windows, walls, the roof, flooring and even gutters, eaves and downpipes.

Bushfire prone areas in Margaret River (shaded pink). Property owners in the bushfire prone areas will have to comply with new building standards from April this year. Photo: Supplied

The foundation behind the standards is the Bushfire Attack Level (BAL) rating system. Under the system, there are six categories, from BAL low to the highest level – BAL flamezone.

Large tracts of land in many WA towns and cities have been assessed as within bushfire prone areas and will be affected.

The changes were introduced following the 2011 Perth Hills fire which destroyed 71 homes. A State government inquiry made dozens of recommendations, including the introduction of the new fire safety standards.

Johnston Road in Yarloop after the fires. Photo: nearmap

But not all builders are happy with the changes.

Summit Homes South West general manager David Hunt says the standards will cost some new home owners dearly – by as much as $100,000 in extreme fire areas.

Some products specified under the new ratings are not even available in WA yet, he said.